In one type of thermal printer which prints colored images, a carrier contains a repeating series of spaced frames of different colored heat transferable dyes. In such apparatus, the carrier is disposed between a receiver, such as coated paper, and a print head formed of, for example, a plurality of individual heating elements. When a particular heating element is energized, it is heated and causes dye from the carrier to transfer to the receiver. The density or darkness of the printed color dye is a function of the energy delivered from the heating element to the carrier.
Thermal dye transfer printers offer the advantage of true "continuous tone" dye density transfer. This result is obtained by varying the energy applied to each heating element, yielding a variable dye density image pixel on the receiver.
One type of thermal printer uses resistive ribbons. In U.S. Pat. No. 4,434,356 assigned to the IBM Corporation, a circuit is described which provides constant current to a resistive ribbon carrier. Resistive ribbon printing technology uses a carrier which includes a metal conducting layer and a dye layer containing a dye to be transferred to a receiver. Current is supplied to the carrier by an electrode or array of electrodes and returns to ground via the conductive layer. The electric current is converted to heat through the resistive heating of the carrier. The heat causes dye to transfer to a receiver.
In the print head for such printers, a plurality of spaced conductive electrodes are secured to a substrate such as shown in U.S. Pat. No. 4,684,960. A problem with the electrodes is that they frequently wear unevenly and consequently make poor electrical connection to the carrier. Hardness of the low electrical resistivity electrodes has been shown to be an important consideration for wear resistance, and metals of high hardness such as molybdenum and tungsten, are preferred. However, these probe materials have to be refurbished at intervals by abrasively polishing the probes provide for proper contact with the carrier.
With faster printing speeds and higher temperatures at the probe interface, the uneven wear of the electrodes becomes a functional constraint and a low electrical resistivity probe material of higher hardness and wear resistance is required, to reduce or eliminate the need for frequent refurbishing of the electrode.
After a number of prints have been made, the surfaces of the substrate and electrodes which contact the carrier must be ground smooth by an abrasion wheel made of diamond, silicon carbide, aluminum oxide or the like.